Substance use disorders are highly comorbid with HIV infection, with nearly 25% of individuals with HIV needing treatment. With the success of combinatorial antiretroviral therapies (cART), HIV-associated mortality has substantially declined. This has resulted in a growing population of chronically HIV-infected and cART treated adults in the United States. Both HIV infection and cART may interact with drug exposure to alter neurobiology, thus creating a behaviorally and biologically distinct condition and requiring novel, targeted pharmacotherapeutic strategies to reduce the compulsive drug use and high relapse propensity that characterize substance use disorders. The corticostriatal glutamate system is a key regulator of these forms of behavioral inflexibility. Projections from the medial prefrontal cortex to the nucleus accumbens are critical mediators of reinstatement of drug seeking, a model of relapse, and the inability to terminate drug seeking despite adverse consequences, a model of compulsivity. A growing literature in both HIV patient populations and preclinical models has identified infection-induced alterations in the corticostriatal glutamate system as a contributor to HIV-associated neurocognitive disorders. Despite this, a robust characterization of corticostriatal glutamate system alterations in HIV infection and cART treatment, with circuit- and cell-type specificity, is lacking. We will capitalize on the advent of new mouse models of HIV infection and perform studies in parallel in (1) a humanized mouse model that successfully develops human-like microglia, thus enabling progressive central nervous system infection with HIV, and (2) wild-type mice infected with a chimeric virus ? EcoHIV. To determine whether current industry standards of treatment impact behavior or glutamate system biology independently or in combination, a subset of mice will receive chronic bictegravir, emtricitabine, and tenofovir alafenamide (B/F/TAF) treatment. This research will use multiplexed in situ hybridization to test the hypothesis that gene and protein expression are altered in glutamate neurons and astrocyte populations in mouse models of HIV infection and cART. We will also test the hypothesis that HIV infection and B/F/TAF interact to regulate astrocyte and neuron calcium signaling during cocaine reward learning, cocaine reinstatement, and compulsive-like cocaine seeking via simultaneous fiber photometric assessment in corticostriatal astrocytes and neurons. To demonstrate a role for gliotransmission and glutamatergic corticostriatal neuron activity in reducing compulsive-like or relapse-related cocaine seeking in mice, we will use cell- and circuit-specific chemogenetic manipulations. Finally, we will use novel and preclinically-validated pharmacological tools for regulating glutamate release and uptake in humanized, HIV-infected and EcoHIV-infected mice to determine whether pharmacological strategies to reduce compulsivity and relapse are similarly effective in infected and B/F/TAF-treated states. My lab will address this unmet need through collaboration with leaders in the immunology, HIV, and drug discovery fields, enabling us to provide thorough, convergent data on corticostriatal glutamate regulation of drug seeking in HIV infection.